It would be nice if your truck only had to run where daytime temperatures hovered around 70°F and nights never dipped below 50°F. A big lottery win would be nice too.
Fact is, average ambient temperatures vary tremendously across the continent – even within a single province or state – so you’ll need to plan for wild temperature swings if your driving takes you to all corners. It’s an important part of both reliability and fuel conservation, particularly at the cold end.
From a fuel economy standpoint, the temperature has to dip below freezing to have any measurable impact. But it will, and at least a 0.5 to 1.0 mpg drop in winter is to be expected. The cold affects fuel usage in a number of ways:
• The colder the air, the denser it gets. And the denser the air, the harder it is for trucks to cut through. Tests by Detroit Diesel show a 2% loss in fuel economy with every 10°F drop in temperature. So if you get 7.0 mpg running in 70° temperatures, don’t expect much more than 6.0 mpg in 0° temperatures.
• Lubes in transmissions, drivelines, axles, and wheel ends get thicker. They need more horsepower to turn and that means higher fuel use.
• Rolling resistance increases as tires get cold and lose air pressure on roads covered with ice or snow. Also, frozen parking brakes can create additional drag.
• Blended fuels tend to have less energy content, so it takes more fuel to drive the same distance.
• Extra idling, to keep the engine and cab warm, sucks up fuel with the truck odometer at a standstill.
Watch Your Fuel
Diesel is one of the most efficient sources of energy on the planet. It’s relatively heavy, ranking below aviation fuel, gasoline, and kerosene, and just above tar and sludge.
Its weight gives it more BTUs – more potential energy – than the lighter fuels, (see the ‘Fuel Basics’ sidebar). And the more energy in a gallon of fuel, the more miles you can drive. The downside is that heavier fuels contain more paraffin wax. That wax normally stays dissolved, but as the temperature drops it crystallizes.
The colder it gets, the larger the wax globs and the slower the fuel flows. Eventually, it solidifies or gels, and won’t move at all.
The temperature at which wax first begins to form is called the cloud point (so-named because the fuel begins to cloud or haze). The temperature just before the fuel solidifies (usually 5° above that point) is called the pour point. An engine may still run after fuel reaches the cloud point, but eventually wax will clog filters and lines and starve you to a stall.
Cloud & Pour Points
Cloud and pour points are all over the map. Oil companies blend fuel differently in different areas of the country at different times of the year. In its preferred specs for #2 diesel (RP 309), The Technology & Maintenance Council of the American Trucking Associations (TMC) recommends a cloud point 5° to 10° and a pour point 20° to 25° below expected ambient temperature.
There are several ways to ensure that fuel meets these limits:
• Buy a winter fuel blended with kerosene, usually labeled #1 diesel. Since kerosene is lighter and contains less paraffin, it depresses pour point. But since lighter fuels have less energy, fuel mileage will suffer. Expect at least a 1% drop in fuel economy with every 10% of added kerosene. If you run a lot of hills, expect an even greater loss. Also, remember that all winter fuels blends aren’t the same. A 40/60 blend bought in Mississippi may not be the same as a 40/60 Manitoba.
• Blend special winter additives with standard #2 diesel. The key is knowing what you’re adding. Additives have the most impact on the pour point. And they’re most effective when added before it gets too cold. If you run into unexpected cold weather, you can attack clouded fuel by overdosing with additives. But remember, the more additives, the lower the fuel economy.
• Buy fuel regionally. Meaning, you can get into trouble buying fuel in, say, South Carolina, and then traveling home to Moncton.
Wax isn’t the only cold-weather item that clogs up fuel lines and filters. Water in fuel will freeze and create barriers. Low-quality fuel often has water in it. As well as reducing fuel mileage, it can create enormous headaches in cold weather. To avoid taking on water, buy good quality fuel from a reputable supplier. It may be a few cents per gallon higher, but you’ll save a lot more in the long run.
Water that condenses in tanks and lines can be handled with a fuel/water separator and filters.
Role of Heaters
You may choose to use heaters in place of buying winter fuel or using fuel additives. But they must be mounted wisely, and you ought to consult your engine supplier before you do anything at all.
Fuel can basically be warmed two ways: With the engine coolant or with an electrical heater. Coolant heaters circulate heated coolant around fuel lines or into fuel tanks. They’re favored because high-capacity electric heaters can drain batteries. The downside of coolant heaters is that they need a supplemental heating device when the truck has been sitting in the cold. Waxed and/or iced fuel needs to be warmed before start-up with small electrical preheaters on filters and fuel lines, a fuel-fired coolant heater, or an electric block heater.
Mounting is crucial. In-line types should be mounted as close as possible to the fuel filter. The further downstream they are, the more heat is required to overcome heat lost through the line to the filter.
If you only use an in-tank heater, it must be able to heat fuel well above its cloud point to compensate for heat lost in the filter line. In-tank heaters should be mounted close to the fuel outlet and regulated so that fuel temperature never exceeds 100°.
Modern diesels provide pretty reliable cold starts because fuel injection rates are very precise, but they may still need help when it gets chilly. Diesel doesn’t ignite until it reaches 725°F, and when ambient temperatures drop below 40°F you can’t reach this temperature simply by compressing air in the cylinder. To ensure faster cold starts, you’ve got choices:
• Use an ether-based starting fluid. Ether ignites at about 350°F. When injected into the cylinder during cranking, it creates a temperature high enough to ignite the diesel. The ether can be injected manually with an aerosol can or with an engine-mounted system. A fully automatic system which meters just the right amount of ether is ideal. Operators who inject manually often use too much, leading to possible engine damage.
• Spec an engine heater. These can be coolant, electrical, or fuel-fired types. Some heat the block, others the intake manifold, and some the oil pan. The idea is to preheat the engine or the intake air so that fuel ignites quickly and the engine runs efficiently sooner.
• Spec an exhaust brake that also preheats the engine. By restricting exhaust during startup, combustion temps rise quickly, allowing a more complete burn.
• Check the thermostat. A thermostat that fails to open or leaks coolant to the radiator will slow warm-up and hasten cooldown.
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